1. Field of the Invention
The present invention relates to a hydraulic system for a leveling apparatus in excavator and forestry equipment, and more particularly to an improved hydraulic system for a leveling apparatus in excavator and forestry equipment, whereby an upper frame of the equipment is kept in a horizontal state even if a lower frame of the equipment is on an inclined ground against a horizontal surface H.
2. Description of the Prior Art
Conventionally, since an excavator or heavy equipment, such as a tree harvester, a tree feller, or the like, performs a work or moves on an inclined ground, such as a slope, a hill, or the like, against a horizontal surface H, an upper frame of the equipment may be tilted to one side or may overturn due to the inclination of the ground. Accordingly, a leveling apparatus is separately installed between the upper frame and a lower frame to keep the horizontal level of the upper frame uniform.
U.S. Pat. No. 6,609,581 assigned to Tigercat Industries Inc. discloses a leveling mechanism using two actuators. According to the technology disclosed therein, the leveling of equipment is maintained by tilting an upper frame around one tilt shaft on a lower frame provided in a lower frame using the two actuators. However, this technology has the drawback in that a great load is applied to the actuators in accordance with the tilt of the equipment or the upper frame, and thus the manufacture and maintenance/repair of the equipment becomes difficult.
As another leveling system, U.S. Pat. No. 6,173,973 assigned to Timberjack Inc. discloses a leveling mechanism for a forestry machine. According to this technology, one tilt shaft is provided on a frame of a lower frame using four actuators, and the actuators are link-coupled to the tilt shaft and a turntable to tilt an upper frame in every direction. According to this technology, however, since the actuators are arranged to be inclined inside the lower frame and the tilt is performed along with a journal shaft and a link structure, the tilt range of the upper frame may lean upon an inclined ground in the forward/backward direction or an inclined ground in the left/right direction of the equipment, and this makes the control of load required in the actuators difficult. The respective actuators should be separately controlled.